Unraveling the multiple facilitative effects of consumers on marine primary producers

IF 4.4 2区 环境科学与生态学 Q1 ECOLOGY Ecology Pub Date : 2024-10-02 DOI:10.1002/ecy.4439
Matthew E. S. Bracken, Genevieve Bernatchez, Alexander J. Badten, Rachel A. Chatfield
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Abstract

The loss of consumers threatens the integrity of ecological systems, but the mechanisms underlying the effects on communities and ecosystems remain difficult to predict. This is, in part, due to the complex roles that consumers play in those systems. Here, we highlight this complexity by quantifying two mechanisms by which molluscan grazers—typically thought of as consumers of their algal resources—facilitate algae on rocky shores. Initial observations in high-zone tide pools revealed that both water-column ammonium concentrations and photosynthetic biomass were higher in pools containing higher densities of grazers, suggesting that local-scale nutrient recycling by the grazers could be enhancing algal biomass. We assessed this possibility by experimentally manipulating grazer abundances at the level of whole tide pools but controlling access of those grazers to experimental plots within each pool. Contrary to predictions that algal biomass inside grazer exclusions would increase as grazer abundances in the pools increased, we found that algal biomass inside grazer-exclusion fences was unaffected by grazer abundances. Instead, the consumptive effects of grazers that were evident at low grazer abundances transitioned to facilitative effects as experimentally manipulated grazer abundances increased. This finding suggested that these positive interactions were associated with the physical presence of grazers and not just grazers' effects on nutrient availability. Subsequent experiments highlighted the potential role of “slime”—the pedal mucous trails left behind as the mollusks crawl on the substratum—in promoting the recruitment of algae and thereby mediating a spatial subsidy of new organic matter into the system. Furthermore, different grazer groups contributed disproportionately to ammonium excretion (i.e., turban snails) versus slime production (i.e., littorine snails), suggesting a potential role for grazer diversity. Our work highlights the complex ways in which consumers affect their resources, including multiple, complementary mechanisms by which these grazers facilitate the algae they consume.

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揭示消费者对海洋初级生产者的多重促进作用。
消费者的丧失威胁着生态系统的完整性,但其对群落和生态系统的影响机制仍然难以预测。部分原因是消费者在这些系统中扮演着复杂的角色。在这里,我们通过量化软体动物食草动物(通常被认为是藻类资源的消费者)促进岩岸藻类生长的两种机制来强调这种复杂性。对高区潮池的初步观察显示,在食草动物密度较高的潮池中,水柱铵浓度和光合生物量都较高,这表明食草动物在局部范围内进行的营养循环可能会提高藻类的生物量。我们通过实验在整个潮池水平上操纵食草动物的丰度,但控制这些食草动物进入每个潮池中的实验地块,从而评估了这种可能性。我们预测,随着潮池中食草动物数量的增加,食草动物排斥区内的藻类生物量也会增加,与此相反,我们发现食草动物排斥栅栏内的藻类生物量不受食草动物数量的影响。相反,随着实验操控的食草动物丰度的增加,食草动物在食草动物丰度较低时明显的消耗效应会过渡到促进效应。这一发现表明,这些积极的相互作用与食草动物的实际存在有关,而不仅仅是食草动物对养分供应的影响。随后的实验强调了 "粘液"--软体动物在底层爬行时留下的足部粘液痕迹--的潜在作用,即促进藻类的繁殖,从而为系统提供新的有机物质。此外,不同的食草动物群对氨的排泄(即头巾螺)与粘液的产生(即小蜗牛)的贡献不成比例,这表明食草动物的多样性具有潜在的作用。我们的研究强调了消费者影响其资源的复杂方式,包括这些食草动物促进其所食用藻类的多种互补机制。
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来源期刊
Ecology
Ecology 环境科学-生态学
CiteScore
8.30
自引率
2.10%
发文量
332
审稿时长
3 months
期刊介绍: Ecology publishes articles that report on the basic elements of ecological research. Emphasis is placed on concise, clear articles documenting important ecological phenomena. The journal publishes a broad array of research that includes a rapidly expanding envelope of subject matter, techniques, approaches, and concepts: paleoecology through present-day phenomena; evolutionary, population, physiological, community, and ecosystem ecology, as well as biogeochemistry; inclusive of descriptive, comparative, experimental, mathematical, statistical, and interdisciplinary approaches.
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